1. Field of the Invention
The invention relates to a programmable clock generator, more particularly to a programmable clock generator used in dynamic-voltage-and-frequency-scaling (DVFS) operated in Sub- and Near-Threshold region.
2. Description of the Prior Art
The wireless behavior sensor network technology has already occupied an important influence in life gradually. Under current energy conservation and environmental protection consciousness mainstream, all big technological factories study the methods for reducing energy consumption, and also try to lengthen the working time of the apparatus at the same time. Thus, the design of extremely low voltage circuit becomes very important in order to reach the technology of extremely low power consumption. Therefore, how to operate the circuit near sub-threshold region has become a very important issue.
Due to the advanced progress of Complementary Metal-Oxide-Semiconductor (CMOS) process, the thickness of gate-oxide layer becomes much thinner in the transistor. It can only bear much less voltage, including the gate-source voltage (Vgs) and the gate-drain voltage (Vgd). In order to increase the working speed of the circuit, and reduce the energy consumption, the working voltage is also reduced for the design of recent integrated circuit. In the conventional traditional technology, in order to reduce the power consumption of circuit, it is often necessary to reduce the operation voltage and frequency of circuit. Under low voltage, the power consumption of apparatus can be reduced greatly, because the dynamic power consumption is reduced by two orders. However, under extremely low voltage, the circuit is influenced by the variation of process, voltage and temperature greatly, so that the frequency locking range of clock generator will be changed. When the frequency locking range is unable to cover the reference frequency, the clock generator might be unable to be operated due to the functional error of circuit.
Thus, it is necessary to develop a programmable clock generator, which is able to be operated under extremely low voltage in order to compensate the variation of process, voltage and temperature.